Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$165.58	10.852%	$183.5487	$183.55	$183.55	$183.50
Purchase #2	$141.80	3.142%	$146.2554	$146.26	$146.25	$146.30
Purchase #3	$56.39	5.630%	$59.5648	$59.56	$59.55	$59.60
Purchase #4	$74.78	11.849%	$83.6407	$83.64	$83.65	$83.60
Purchase #5	$74.32	11.840%	$83.1195	$83.12	$83.10	$83.10
Purchase #6	$12.73	6.552%	$13.5641	$13.56	$13.55	$13.60
Purchase #7	$240.88	3.113%	$248.3786	$248.38	$248.40	$248.40
7 purchase totals =	$766.48		$818.0718	$818.07	$818.05	$818.10